The present invention is related to an device for controlling an amount of light transmitted from a light source of a video processor which functions as a lighting unit for an endoscope.
In an endoscope, light is transmitted from a light source using a light wave guide, such as an optical fiber cable, in order to illuminate an object to be observed. In order to adjust the brightness of the observed image, a device for controlling an amount of light transmitted from a light source to an incident surface of the light wave guide, is employed. In a conventional endoscope, the light amount controlling device has a light shield which is rotated about an axis by a stepping motor. The rotation of the light shield controls the amount of light from the light source that is incident on the incident surface of the optical fiber cable. With this type of light amount controlling device, the brightness of the observed image is detected periodically. Then, the position of the light shield is adjusted such that the brightness of the observed image is within an allowed brightness range.
Conventionally, the amount of light transmitted from the light source to the endoscope is controlled by applying the same number of pulses to the input of the stepping motor during each interrupt procedure (see FIG. 11A). Therefore, the stepping motor and the light shield are rotated by the same angular amount during each interrupt procedure. The process of detecting the brightness level, and driving the stepping motor to rotate the light shield is repeated until the detected brightness is again within the allowed brightness range.
However, in the conventional endoscope, since the number of driving pulses sent to the motor is constant during the execution of each interrupt procedure, if the number of pulses is set to a relatively small value, then the light shield will be moved slowly. This results in an increase in the response time of the light amount controlling device.
As shown in FIG. 11A, for example, each drive pulse rotates the motor 0.5 degrees, three drive pulses are sent during each interrupt, and the interrupts are executed every 50 ms. Thus, in order to rotate the stepping motor 10 degrees, seven interruption procedures are required for a total time of 0.35 seconds. Further, since the number of pulses must be in multiples of three, the number of drive pulses cannot be 20, the optimum number, but must be 18 or 21. Therefore, the light shield cannot be moved to the optimum position.
In order to decrease the response time of the light amount controlling device, the number of driving pulses sent to the stepping motor can be increased. However, in this case, the light shield will be moved through a large angle of rotation and thus it may not be possible to adjust the amount of light such that the brightness level falls within the allowed brightness range. This will result in the control system becoming unstable with unwanted back-and-forth oscillations (hereinafter referred to as hunting) occurring.
Further, as different types of endoscopes have different allowed brightness ranges, different numbers of driving pulses are required in order to properly adjust the amount of light transmitted from the light source.
Furthermore, for one type of endoscope, if the sending of a predetermined number of pulses to the stepping motor does not cause hunting, in another endoscope, the predetermined number of pulses may not be sufficiently low, and hunting may occur. Therefore, since the light source may be connected with various types of endoscopes, the number of pulses may be set to the minimum number required for all types of endoscopes in order to avoid the hunting problem. As a result, the speed at which the brightness level can be adjusted for the types of endoscopes where hunting is not a problem, will be reduced.
It is therefore an object of the present invention to provide a device for controlling an amount of light of a lighting unit for an endoscope, in which the amount of light can be adjusted quickly, and accurately, and hunting can be prevented.
According to one aspect of the present invention, there is provided a device for controlling an amount of light of a lighting unit for an endoscope, the endoscope being used to view an image of an object. The device includes means for shielding light, generated by a light source and transmitted to the endoscope, a stepping motor for driving the light shielding means, the stepping motor driving the light shielding means for a plurality of predetermined time intervals, and means for detecting a brightness of the image, the brightness of the image being detected during each of the predetermined time intervals. Pulses are generated during each of the predetermined time intervals, a number of the pulses generated being used to control an amount of driving of the stepping motor in each of the plurality of predetermined time intervals. The number of pulses generated by the pulse generating means is determined in accordance with a difference between the brightness of the image detected during each of the predetermined time intervals and a desired brightness of the image.
Therefore, a different number of pulses is generated when the difference in brightness of the detected image and the desired brightness changes. Preferably, when the brightness difference is large a large number of pulses is generated, and therefore the light shielding means is moved quickly. Then when the brightness difference is small, and the detected brightness is almost within an allowed brightness range, the number of pulses generated is small. Therefore, the light shielding means is moved in smaller steps and hunting can be prevented.
In a preferred embodiment, there is a memory for storing a first table of numbers of pulses to be generated corresponding to a plurality of brightness ranges, each of the brightness ranges being a range of differences between the detected brightness of the image and the desired brightness of the image. The memory can be a ROM or other static memory. Further, there is a unique number of pulses stored for each brightness range. Therefore, depending on the difference in brightness between the detected image and an input brightness level set by an operator, the number of pulses sent to the stepping motor will be different.
Since, many types of endoscopes may be used with the lighting unit, the memory of the preferred embodiment stores a second table of numbers of pulses to be generated corresponding to the plurality of brightness ranges. The second table of numbers of pulses is different from the first table of numbers of pulses, and corresponds to another type of endoscope.
Further, the device includes a selector for selecting one of the first table of numbers of pulses and the second table of numbers of pulses.
In one preferred embodiment, the endoscope has a memory for storing the type of the endoscope. The selector selects one of the first table and the second table in response to the type of the endoscope stored in the memory.
This allows for easy selectability of the endoscope and facilitates operation of the device when used with the respective endoscope. Furthermore, the device is optimized for each endoscope that is attached thereto.
In another preferred embodiment, the selector is manually actuable for selecting the type of endoscope.
According to a second aspect of the present invention, there is provided a device for controlling a device for controlling an amount of light of a lighting unit for an endoscope, the endoscope being used to view an image of an object. The device includes means for shielding light, generated by a light source and transmitted to the endoscope, a stepping motor for driving the light shielding means, the stepping motor driving the light shielding means by a predetermined driving amount for a plurality of time intervals, and means for setting a duration of the time interval to have one of a plurality of time values.
Therefore, by changing the time interval for driving the light shielding means, the time required for adjusting the amount of light can be reduced, even if the amount of driving of the stepping motor is made small in order to prevent hunting.
In a preferred embodiment, the endoscope type is stored in a memory and the duration of the time interval is set in accordance with the type of the endoscope. Therefore, the operation of the device can be optimized for each type of endoscope.
In another preferred embodiment, the time interval is set in accordance with the position of a manually operable switch. This adds flexibility to the operation of the device, and allows operation to be optimized for endoscopes that do not have the type stored in a memory.
According to a third aspect of the present invention, there is provided a device for controlling an amount of light of a lighting unit for an endoscope, the endoscope being used to view an image of an object. The device includes means for shielding light, generated by a light source and transmitted to the endoscope, a stepping motor for driving the light shielding means, the stepping motor driving the light shielding means for a plurality of predetermined time intervals, and means for detecting a brightness of the image, the brightness of the image being detected during each of the predetermined time intervals. A predetermined number of pulses is generated during each of the predetermined time intervals, the predetermined number of pulses being transmitted to the stepping motor during each of the predetermined time intervals. An angular position of the light shielding means is determined, and a phase of excitation of the stepping motor is varied in response to the determined angular position.
Therefore, by changing the number of phases of excitation of the stepping motor, the drive amount of the stepping motor in a given predetermined time interval can be changed.
In a preferred embodiment the stepping motor is driven with 2 phase excitation when the angular position is less than or equal to a predetermined angular position. Otherwise, the stepping motor is driven with 1-2 phase excitation (i.e., excitation alternating between single phase and two phase excitation at every pulse).
In another preferred embodiment, the phase of excitation of the stepping motor is further varied in response to the detected brightness of the image. In this case, even if the angular position is greater than the predetermined angular position, if the brightness of the image is larger than a predetermined value, the stepping motor is driven with 2 phase excitation, in order to improve the speed at which the amount of light is reduced in order to bring the detected image brightness into an allowed brightness range.
In another preferred embodiment, the phase of excitation of the stepping motor is varied in response to the endoscope type. This optimizes the performance of the device for each type of endoscope.
According to a fourth aspect of the present invention, there is provided a device for controlling an amount of light of a lighting unit for an endoscope, the endoscope being used to view an image of an object. The device includes means for shielding light, generated by a light source and transmitted to the endoscope, a stepping motor for driving the light shielding means, the stepping motor driving the light shielding means for a plurality of predetermined time intervals, means for detecting a brightness of the image, the brightness of the image being detected during each of the predetermined time intervals, and means for inputting one of a plurality of desired brightnesses of the image. A predetermined number of pulses is generated during each of the predetermined time intervals, the predetermined number of pulses being transmitted to the stepping motor. One of a plurality of allowed brightness ranges of the image is set in accordance with the input desired brightness of the image. Then, the device determines whether the detected brightness is within the set allowed brightness range.
Therefore, in a preferred embodiment, when the desired input brightness of the image is high, the allowed brightness range is large, since the change in brightness of the image per unit rotation of the light shielding means is small, and therefore, the number of time intervals required to adjust the amount of light such that the detected image brightness is within the allowed brightness range, is reduced.
In another preferred embodiment, an angular position of the light shielding means is determined, and the allowed brightness range is set in response to the determined angular position of the light shielding means.
In yet another preferred embodiment the type of endoscope is determined and the allowed brightness range is also set in response to the determined endoscope type.
According to a fifth aspect of the present invention, there is provided a device for controlling an amount of light of a lighting unit for an endoscope, the endoscope being used to view an image of an object. The device including means for shielding light, generated by a light source and transmitted to the endoscope, a stepping motor for driving the light shielding means, the stepping motor driving the light shielding means for a plurality of predetermined time intervals, means for detecting a brightness of the image, the brightness of the image being detected during each of the predetermined time intervals, means for inputting a desired brightness of the image. Pulses are generated during each of the predetermined time intervals, a number of the pulses generated being used to control an amount of driving of the stepping motor in each of the plurality of predetermined time intervals. The number of pulses generated by the pulse generating means is determined in accordance with the input desired brightness of the image.
Therefore, since the change in brightness per unit rotation of the light shielding means increases as the brightness of the image decreases, when the input brightness level is high, the light shielding means can have a higher driving amount than when the brightness of the image is low. This will improve the speed at which the amount of light can be adjusted, without introducing a hunting problem.
Alternatively, the number of pulses generated can be determined in accordance with an angular position of the light shielding means.
Optionally, the number of pulses generated can be further determined in accordance with the type of endoscope.
According to a sixth aspect of the present invention, there is provided a device for controlling an amount of light of a lighting unit for an endoscope, the endoscope being used to view an image of an object. The device includes means for shielding light, generated by a light source and transmitted to the endoscope, a stepping motor for driving the light shielding means, the stepping motor driving the light shielding means for a plurality of predetermined time intervals, means for detecting a brightness of the image, the brightness of the image being detected during each of the predetermined time intervals, and means for detecting hunting of the stepping motor. Pulses are generated during each of the predetermined time intervals, a number of the pulses generated being used to control an amount of driving of the stepping motor in each of the plurality of predetermined time intervals. A number of pulses generated by the pulse generating means during each of the predetermined time intervals is determined in response to hunting being detected by the hunting detecting means, the determined number of pulses being reduced when the hunting is detected.
Therefore, in case hunting is detected, by reducing the number of pulses sent to the stepping motor, the driving amount of the stepping motor is reduced, and the hunting problem can be overcome.
Optionally, the device determines whether the brightness of the image is larger than a desired brightness of the image, and outputs a first value if the detected brightness is larger than the desired brightness, and outputs a second value if the detected brightness is not larger than the desired brightness. Each output value is stored in a register of a memory. The device then determines if hunting occurred by examining the registers of the memory. If the registers sequentially store an alternating pattern of the first and second values, then hunting is occurring.
By using a memory to store the information, the detection that hunting is occurring can be done more quickly, since the response time of the stepping motor does not effect the detection of hunting.
Alternatively, data related to a direction (i.e., forward and reverse) of driving the stepping motor can be stored in a register of another memory. If the registers sequentially store an alternating pattern of the forward and reverse data, then hunting is occurring.
According to a seventh aspect of the present invention, there is provided a device for controlling an amount of light of a lighting unit for an endoscope, the endoscope being used to view an image of an object. The device includes a plurality of light shields for shielding light generated by a light source and transmitted to the endoscope, a stepping motor for driving the plurality light shield means, the stepping motor driving the plurality of light shields for a plurality of predetermined time intervals, means for detecting a brightness of the image, the brightness of the image being detected during each of the predetermined time intervals. A predetermined number of pulses is generated during each of the predetermined time intervals, the pulses generated being used to control an amount of driving of the stepping motor in each of the plurality of predetermined time intervals. A differences between the brightness of the image detected and a desired brightness of the image determines which of the plurality of light shields is to be driven by the stepping motor.
Therefore, if the difference in brightness is large, two or more light shields may be moved, thereby increasing the speed at which the amount of light is varied. Conversely, if the difference in brightness is small, then only one light shield is needed to be moved in order to bring the detected image brightness into an allowed brightness range. Since the number of light shields driven can be changed at each time interval, the amount of light can initially be varied quickly, and then varied accurately in order to prevent hunting.
Alternatively, light shields having different effects on the change in brightness per degree of rotation can be employed. In this case, the light shield which has the greatest effect on the change in brightness per degree of rotation is driven in order to quickly change the detected image brightness. Then another light shield having less effect can be driven in order to change the detected image brightness more accurately, until the detected image brightness is in the allowed brightness range.
In the preferred embodiments, the light shields are arranged to be rotated on different axis of rotation.